KAMPALA, Uganda -- An al-Qaeda-linked Somali militia claimed responsibility Monday for back-to-back bombings in the Ugandan capital that killed at least 74 people watching the World Cup final on television, marking the first major international attack by the group in a region where the United States and its allies are attempting to stem the rise of Islamic radicalism.

In the Somali capital, Mogadishu, a top spokesman for the hardline al-Shabab said the group carried out the bombings, and he threatened further attacks if Uganda and Burundi continued to supply troops to an African Union peacekeeping force in Somalia.

"Al Shabab was behind the blasts," Ali Mohamud Raghe, the militia's spokesman told reporters. "Thanks to our martyrs who carried out the attacks."

The powerful explosions tore through two venues in Kampala where crowds were watching broadcasts of the World Cup final late Sunday, killing at least 74 and wounding scores of others, Ugandan police said. At least one American was killed and several were wounded, according to the U.S. Embassy here.

The bombings unfolded at the Kyadondo Rugby Club and at the Ethiopian Village restaurant where hundreds of boisterous and cheering soccer fans, including clusters of foreigners, had gathered to watch Spain beat the Netherlands in the final in South Africa.

Among the dead at the rugby club was Nate Henn, 25, of Wilmington, Del., a worker for Invisible Children, a California-based aid group that helps child soldiers, the group said on its Web site. A 16-year-old girl from Ellicott City, Md., Emily Kerstetter, was injured, according to WMAR-TV in Baltimore. She was in Kampala with her grandmother's church group from Pennsylvania.

Ugandan Police Chief Kale Kaihura immediately pointed blame at al-Shabab, a hard-line militia with growing ties to al-Qaeda that has perpetrated several bombings in recent months in Somalia.

Last week, the militia's top leader, Mukhtar Abdurahman Abu Zubeyr, accused African Union peacekeeping forces in Mogadishu of committing "massacres" against Somalis. Ugandan and Burundian troops make up the peacekeeping force. Abu Zubeyr warned that his forces would take revenge against the peoples of Uganda and Burundi.

Uganda, a key U.S. ally, is also a training ground for soldiers for Somalia's transitional government, which al-Shabab is seeking to overthrow. The training program is backed by the United States and European nations. The United States officially considers al-Shabab a terrorist organization.

The militia, which seeks to create an Islamic emirate and has imposed Taliban-like dictates, has banned playing soccer in many areas and prohibited broadcasts of the World Cup, describing the sport as "a satanic act" that corrupts Muslims.